Downhole drills suffer considerable exposure to erosive conditions in that air or other fluid entrained rock solids are passed along the outside of the drill on their way out of the drill hole. Erosive damage to the drill is a common cause of drill failure. Drill chucks which hold the working drill bit are particularly vulnerable to such damage in that they are located in close proximity to the transition zone between the drill face, where the rock is cut, and the walls of the drilled hole where air flow is most erratic.
The chucks for downhole drills have historically been of one (1) piece design. The material selection has been a compromise between the mechanical requirements of the spline/thread area and the erosive resistance requirement of the collar.